单选题 The term "tides" has come to represent the cyclical rising and failing of ocean waters, most notably evident along the shoreline as the border between land and sea moves in and out with the passing of the day. The primary reason for this constant redefinition of the boundaries of the sea is the gravitational force of the moon.
This force of lunar gravity is not as strong as Earth's own gravitational pull, which keeps our bodies and our homes from being pulled off the ground, through the sky, and into space toward the moon. It is a strong enough force, however, to exert a certain gravitational pull as the moon passes over Earth's surface. This pull causes the water level to rise(as the water is literally pulled, ever so slightly, toward the moon) in those parts of the ocean that are exposed to the moon and its gravitational forces. When the water level in one part of the ocean rises, it must naturally fall in another, and this is what causes water levels to change, dramatically at times, along any given piece of coastline.

单选题 Which of the following is the most obvious effect of the tides?
A. A part of the beach that was once dry is now under water.
B. Floods cause great damage during heavy rainstorms.
C. The moon is not visible.
D. Water falls.

单选题 The word "lunar" in the first sentence of paragraph2 most nearly means ______.
A. weak B. strong C. destructive D. related to the moon

单选题 It can be inferred from the passage that if one were to travel to the moon, ______.
A. water would be found on its surface
B. an object, if dropped, would float away from the surface of the moon
C. other planets besides the moon have influence on the tides of Earth's oceans
D. an object, if dropped, would fall to the moon s surface

单选题 The author's primary purpose in writing this passage is to ______.
A. prove the existence of water on the moon
B. refute claims that tides are caused by the moon
C. explain the main cause of the ocean's tides
D. argue that humans should not interfere with the processes of nature